106
FXUS63 KGLD 190928
AFDGLD
Area Forecast Discussion
National Weather Service Goodland KS
328 AM MDT Mon Mar 19 2018
.SHORT TERM...(Today and tonight)
Issued at 327 AM MDT Mon Mar 19 2018
Latest satellite imagery shows the closed low slowly moving east
along the KS/OK border. North of the closed low a large area of
precipitation was rotating around it, moving west. Precipitation
type was heavily dependent on wet bulb temperature. Precipitation
type varied from light snow over the west half or so of the forecast
area to rain over the east.
For the rest of the night and through the morning, the majority of
the precipitation amounts will occur during this timeframe. Rain
will continue to transition to snow from west to east. The band of
frontogenesis near the CO border will fade before sunrise while
another band of frontogenesis forms near Highway 27. This band will
move little and linger through the morning and into the afternoon
then gradually weaken as it moves east. Theta-e lapse rates are
close to being unstable through sunrise then become more stable
during the day. The frontogenesis is not too impressive and the
lapse rates are fairly stable, which gives cause for concern that
snow amounts may be too high from the models, which are two or more
inches above the forecast. However the strongest frontogenesis is
in the dendritic layer which may help negate the effects of the
stable lapse rates.
Given the deep, persistent lift over the east half of the
forecast area today, especially in the dendritic zone, have high
enough confidence of moderate snowfall amounts to expand the
current advisory east. This event does not look like one that
would produce amounts of 3-5 inches. However the strong,
persistent frontogenesis in the dendritic zone is the key. Am
expecting snowfall rates of half an inch an hour or less through
the day, which will add up. The one factor that will reduce
snowfall amounts will be the warm ground temperatures. Looking at
SREF plumes, the members varied from zero to as much as 20 inches
for the same location; confirming that this is a tricky event to
determine snowfall amounts. With all this in mind, am still
concerned that snowfall amounts are on the high side, but would
prefer to error on the side of caution. If the frontogenesis
lingers longer into the afternoon and the closed low is slower to
move east than currently depicted, snowfall amounts will end up
being higher than forecast.
Aside from the snow, north winds will be breezy for the south half
of the forecast area. This may lead to some blowing/drifting snow.
Due to temperatures near freezing the snow should be fairly wet
which will help to minimize the blowing/drifting.
During the afternoon the frontogenesis slides east, causing the snow
to end from west to east. During the afternoon the frongotenesis
will weaken as it moves east, so am expecting only an inch or so of
additional snowfall as a result.
Tonight any remaining snow east of Highway 83 will shift east of
Norton and Graham counties before mid evening. Winds will become
light as the surface high pressure moves through.
.LONG TERM...(Thursday through Monday)
Issued at 227 AM MDT Mon Mar 19 2018
Tuesday northwest winds will become breezy in the afternoon over the
west half of the forecast area. Meanwhile relative humidity values
will fall to around 20% for Cheyenne County CO, Wallace and Greeley
counties. The overlap of breezy winds and low relative humidity
will only be an hour or so during the latter half of the afternoon.
This will need to be monitored incase the window of overlap grows.
Wednesday the winds will be light and temperatures will warm as the
upper levelridge continues to build east onto the Plains.
For the extended period...H5ridge shifting eastward across the
Plains region for Thursday and Thursday night gives way to a quick
moving shortwave that will traverse the region Friday/Friday night.
high pressure returns for the start of the upcoming weekend. The
region will see another couple shortwaves moving fairly quickly
across the region for the latter portion of the weekend into next
week.
For precip...the first system for Fri/Fri night carries more areal
coverage due to its track across the region. Looking for mainly
showers as it passes. Some weak instability could bring a few
isolated trw late in the day...for mainly southern areas. With more
zonal flow over the region Sat night/Sun for the second
shortwave...precip makes only a glancing blow to northern border
zones. Will have light rw transition to light sw for this. The final
system working into the beginning of next week still will only have
low chance pops for a rw/sw mix. Latest GFS/ECMWF runs do lack
consistency for amt of expected QPF...but a rw/sw transition looks
most likely with little to no accum at this time based on expected
temps.
Other potential wx issues/concerns for the extended will be the
potential for near critical Fire Wx conditions for Friday into the
weekend. Those areas not seeing any forthcoming precip will be at
most risk...especially for locales south of Interstate 70. RH
reading will be in the 15-20 percent range w/ winds reaching
criteria...especially for Friday afternoon. The other periods will
be off slightly.
For temps...70s for highs Thursday/Friday will trend down to the 60s
over the weekend and 50s by next week. Overnight lows will trend
from 40s Thursday night to around the mid/upper 20s by next week.
&&
.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1130 PM MDT Sun Mar 18 2018
MVFR/IFR ceilings and rain or a wintry mix of precipitation are
expected at the GLD/MCK terminals through 15-18Z today. VFR
conditions will return this afternoon by 21-22Z. At GLD, NE winds
at 20 knots will become northerly at 20-30 knots with gusts to
35-38 knots by ~09Z this morning and persist through ~18Z, then
decrease to 15-20 knots during the afternoon. At MCK, ENE winds at
15-20 knots will become northerly at 20-30 knots by ~09Z and
persist through 15-18Z, then decrease to 15 knots this afternoon.
&&
.GLD WATCHES/WARNINGS/ADVISORIES...
KS...Winter Weather Advisory until 6 PM MDT /7 PM CDT/ this evening
for KSZ001>004-013>016-029.
CO...Winter Weather Advisory until 6 PM MDT this evening for COZ090-
091.
NE...Winter Weather Advisory until 6 PM MDT /7 PM CDT/ this evening
for NEZ079>081.
&&
$$
SHORT TERM...JTL
LONG TERM...JN
AVIATION...VINCENT